This invention relates to the pyrolysis of carbonaceous materials and, in particular, to a method for improving the energy efficiency of such processes.
Pyrolysis processes are common in industry and a typical example is charcoal production from wood. Because of the widespread location of most wood resources it is uneconomic to operate large continuous retorts for charcoal production due to high wood transport and capital costs. Kilns, which burn part of the charge to provide heat for the process are commonly used but the yield is low as wood is wasted and cycle times extend to some weeks.
Batch retorts are sometimes employed and obviously such retorts must be operated as efficiently as possible as the capital cost is higher than kilns of equal capacity. This requires efficiency in fuel usage as the costs of fuels sourced externally to the wood resource are a major factor in plant economics.
Another serious problem that arises with conventional kilns and retorts is that volatile components evolved in the flue gases from the carbonaceous feedstock contain a wide range of chemical compounds. Such evolution is environmentally undesirable when released to the atmosphere and may be detrimental to health as some volatile components have been identified as carcinogens. Moreover, the unregulated emission of such volatile components represents a waste of a potential fuel because the components if combusted can readily be employed as a fuel resource thus enhancing the economics of the pyrolysis process. Emissions from all kilns and retorts are so heavily laden with moisture that they will not burn without assistance from external fuel.